Howdy Knutters,

Every now and again....not sure its always, will pay more attention....but when the engine is up to temp and the fuel in the tank is hot (going to install and fuel cooler this week) and I stop to fuel up...the engine is hard to start up again....it cranks and cranks but no doughnut. If I use the 'choke' it will fire up and then immediately I can turn the choke off and the bike runs fine. 

Its not so much of problem as a curiosity. Wondering whats going on. There is no fuel temp sensor in the EFI system is there?

floyd wrote:Howdy Knutters,

Say howdy to Kenneth, too.

floyd wrote:Howdy Knutters,

Every now and again....not sure its always, will pay more attention....but when the engine is up to temp and the fuel in the tank is hot (going to install and fuel cooler this week) and I stop to fuel up...the engine is hard to start up again....it cranks and cranks but no doughnut. If I use the 'choke' it will fire up and then immediately I can turn the choke off and the bike runs fine. 

Its not so much of problem as a curiosity. Wondering whats going on. There is no fuel temp sensor in the EFI system is there?

That's right there is no temp sensor in the fuel system. All I can think of is that the ECU thinks the engine is too hot to start (over 113°C) until the turning over gets cooler coolant to the sensor which is on the riser behind the radiator.
How long would you have to leave it sit before it would fire up?

once again, it ONLY happens after a large re-fuel. 

Symptoms are: it just cranks for 10-20 seconds before firing rather than the normal half a second. When the choke is applied in this situation it will fire right up and then I turn the choke immediately off and it runs normal.

could this be a vaccum in tank issue

or a vacuum to fpr  issue

thoughts are when the tank is full it creates a pretty good vacuum as there is not much air to expand in there  
preventing the pump from full blast pressure ...check the vents Floyd  ...in 86 or so models  there are two vents ...one from the drip water collection pipe around the fuel cap surround
\the second picks off the filter basket  ...
both exit the underside of the tank ..usually in two tubes that drip into a cup collector and then to near the swingarm  via a tube

if the one to the fuel basket was blocked ...could this prevent a good pump when hot ?  sounds like you need just a little more to get a start

if you get a chance ...try a pressure meter on the feed line to see what happens during this event ?

ive found some issues with my old fuel regulator ... that might be a contributing issue of low pressure to the injectors

good luck mate

Does it only happen the first time you try to restart after a refuel?

Is the refuel creating an airlock in the fuel lines? This could happen if the fuel is extremely hot and turning to vapour. Using the 'choke' will have the effect of opening the throttle to provide more fuel to compensate.

Makes me wonder could fuel temperature affect the fuel pressure regulator. I believe an airlock would. Sudden introduction of cold fuel, typically stored at 15c, may be creating a partial vacuum inside fuel lines.

RickG mentions the temperature and what happens there is that if the sensor is over 113c then the engine cannot be started. However if the temperature goes over 113c when running that will not cause the engine to cut out. Do you ever have any symptoms of running hot, fan cutting in, temperature light on?  I would expect fan on from time to time and if it never comes on its worth checking why. I had experience in a car where the engine running in extremely hot conditions would show a short but significant temperature rise if the engine was stopped while it was very hot. Hence the warning on turbo engines in particular to ease off a few miles before stopping to let the engine return to normal temperature before turning it off.

The normal running of the bike has a constant flow of fuel back to the tank but as the level drops there is less in the tank and it cannot cool down. The return pipe behind the radiator is in a hot zone and in very hot weather and slow riding or when you stop a huge amount of heat radiates back to the fuel line. My fuel pipe at that point has insulation on it......? Also check the insulation under the tank.